Thermionic translating device and system



June 12, 1934. w. CLAYPOOLE 1,962,427

THERMIONIC TRANSLATING DEVICE AND SYSTEM v Filed Aug. 16 1924 zz- I a 56 E'suy mam/mum 46! W jwvewfoz E Patented June 12, 1934 UNITED STATES PATENT OFFICE} THERIVHONIC TRANSLATING DEVICE AND SYSTEM poration of Delaware Application August 16, 1924, Serial No. 732,381

10 Claims.

This invention relates to thermionic translating devices and systems and it has special reference to apparatus and systems of this character in which alternating current energy may be supplied directly to the heating element or filament.

Heretofore, it has been common practice to provide such systems and devices with three main elements-a filament constituting a cathode, a plate or anode and a controlling grid. The filament is heated by direct current from a so-called A battery or some other form of unidirectional non-pulsating current whereby a relatively steady stream of electrons is emitted, which flows past the grid to the anode that is positively charged from a so-called B battery having its negative terminal connected to the filament and its positive terminal to the anode. There is thus a driving electric force operating on the electronic stream.

In order to supply this filament heating current, large and expensive A batteries are necessary. If dry batteries are employed, they have to be replaced frequently and if storage batteries be used, it is essential to have them recharged at frequent intervals. In either case, the employment of batteries is always bothersome and requires constant care and attention in order to obtain eflicient and reliable operation, while such batteries necessitate considerable space, and furthermore constitute a source of possible injury to household One of the objects of the present invention is to provide a thermionic translating device and system of such character that the use of an A battery may be obviated, and the necessary heating current for the filament derived from the usual alternating current house-lighting circuit.

Another object is to provide such apparatus and systems with an improved type of composite cathode of such construction that it may be heated indirectly by means of a filament in close proximity to and heat-conducting relation therewith, that is supplied directly by alternating current energy from the house-lighting circuit through the agency of a small transformer or other suitable means.

A still further object is to provide such a composite cathode of sufficient heat-storage capacity to insure a substantially constant temperature, and thereby steady electronic emission, despite the fact that alternating current energy is applied directly to the heating filament.

An added object is to provide means for insuring that the potential of the cathode shall be constant and entirely independent of the fluctuations or pulsations of the alternating filament current, and moreover for insuring that the oathode shall be charged negatively with respect to the anode.

Accordingly, the present invention contemplates a thermionic translating device and system comprising not only the usual anode or plate and controlling grid, but also, in its preferred form, a composite and unitary cathode of cylindrical form and embodying a. centrally disposed heating filament, a concentric shield closely surrounding the filament and electrically insulated therefrom, and a cathode proper concentrically arranged around and in close heatconducting relation with the shield but electrically insulated therefrom. The filament is of usual construction and is heated by the direct application of alternating current energy derived from a house lighting circuit or other suitable source. The filament may conveniently be electrically connected to the shield at one end, so that the shield constitutes a part of the alternating current heating circuit. The shield is of such material and size as to posses a relatively great heat-storage capacity whereby the heat transmitted therethrough from the filament to the cathode maintains the cathode surface at a substantially uniform and suitable high temperature. Thus, the variations or fluctuations of temperature arising in the filament are evened out by'the heat-storage shield to the end that the cathode element proper is held at a constant temperature and thus produces a steady emission of electrons. Furthermore, the shield is grounded and thus held at zero potential so that there is no possibility of the cathode being influenced by, or being responsive to, the alternating positive and negative potential fluctuations of the current traversing the filament and shield. The potential of the cathode therefore is con- 95 stant, and being connected to the negative terminal of the B battery, is definitely maintained at a predetermined negative potential with respect to the anode. The composite cathode of thermal element is preferably of small dimensions to enable the cathodic surface to attain the requisite temperature for effective and emcient emission of electrons.

These and other objects of the invention and features by means of which they are attained, 105 will be apparent from the following detailed description of the invention as illustrated in its preferred embodiment in the accompanying drawing, of which:

Fig. 1 is a view, partially in side elevation and 110 partially in section, of a thermionic translating device constructed in accordance with my invention, and

Fig. 2 is a atic view of a system arranged in conformity with my invention.

Fig. 3 is an enlarged sectional view of the electrode structure shown in Fig. 1.

Referring to the drawing:

The thermionic translating device comprises an evacuated tube or vessel 10, within which is contained a plate or anode 12, a grid 14 and a composite cathode comprising a heating filament 16, a shield 18 and a cathode element proper 20. The evacuated vessel or container 10 is of usual construction and is provided with a metallic collar or base 22 through which project the usual stationary contact terminals 24 suitably mounted and sealed therein, to which are connected the usual lead-inwires 26 for electrical connection to the various elements within the vessel 10.

The heating filament 16 preferably comprises a single straight wire of tungsten or the like, although it may be desirable, in some instances, for it to be of helical or coil form. Closely surrounding the filament 16 is the tubular shield 18, composed preferably of tungsten and disposed in concentric relation with the heating filament and in close proximity thereto. The shield 18 is electrically insulated from the filament 16 by suitable means. A thin layer of fused silica upon the inner surface of the shield may be used for this purpose. The shield is cylindrical in form and may either be entirely tubular or may be made from a fiat sheet of metal rolled into cylindrical shape with the ends in close abutting relation. This shield is of such size and material as to constitute a heat-storage body.

Immediately surrounding the shield 18 is a cathode element proper20 which is preferably of tungsten and of similar form to that of the shield. It is usually desirable to activate the cathode surface by means of thoria or some similar substance. The cathode proper is in close heat-conducting relation to the shield, but is electrically insulated therefrom by means of a thin layer of fused silica, either upon the inner surface of the cathode, or the outer surface of the shield. Any other suitable means of insulation may-be employed. The preferable arrangement of the heating filament 16 and shield 18 is to electrically connect the. respective upper ends thereof, by means of the connection 28 in order that both elements may form parts of the heating circuit, although this arrangement is not essential and, if desired, the return circuit for the heating element may constitute a separate or distinct wire or connection disposed immediately outside the shield or in any other convenient location. The shield is provided with a connection or lead-in wire 30 connected to the metallic base 22 of the device for electrical contact with an auxiliary yielding contact terminal 32, suit-, ably provided in a socket 34' that may otherwise be of usual construction. This stationary contact terminal 32 is provided with an outer binding post and nut 36 for external connection to ground. The socket 34 furthermore carries a plurality of contact members 39 of suitable construction and adapted to make electrical contact with the contact plugs 24 when the thermionic device is properly inserted in the socket.

The controlling grid 14 may conveniently comprise a helix or coil of wire concentrically disposed around the cathode element 20, but out of contact therewith. Any other suitable form of .grid may be employed. The grid is surrounded by the anode 12, preferably of tungsten, which may be of a form similar to those of the shield and cathode, and this anode is of course spaced from the grid 14. In order to support the upper ends of the grid and the anode they may be attached to the vessel or container 10 by a drop or small body of fused silica 38. The grid and anode form no part of my present invention except as they enter into combination with the other elements and function in correlation therewith to produce the desired results.

with this form of construction it is possible to utilize a source of alternating current energy, such as the usual house-lighting circuit for heating the filament, although any of the ordinary sources of direct current energy mayalso be employed. In either event, the heat produced by the filament is imparted indirectly to the cathode proper 20 by conduction through the shield 18 whereby the cathode element is maintained at a sufllciently high temperature to create the desired rate of electronic emission. The construction described, however, is particularly adapted for use with a source of alternating current supply inasmuch as the interposition of the shield 18 of relatively great heat-storage capacity between the filamentlfi and cathode 20 serves to even out the slight fluctuations in temperature produced by the alternating or fluctuating character of the energizing current. Moreover, by means of the binding post 36 and the connection from it to the shield, said shield may be grounded, whereby its potential is maintained at zero thereby insuring that the fluctuations or alternations of positive and negative potential in the filament circuit shall not be transmitted to the cathode, which is thereby maintained at a constant uniform potential.

For the purpose of securing the necessary temperature of the cathode surface from which the electronic emission originates, it is desirable that the composite cathode be made of relatively small dimensions, although this is a matter which obviously depends upon several factors which may vary within considerable limits. The essentials to be borne in mind are merely that the composite cathode be so designed as to efficiently and effectively maintain the requisite temperature for the required degree of electronic emission.

Having set forth the construction and general principles of operation of a'preferred embodiment of the invention, reference may be had to Fig. 2, which shows the circuit connections of a typical radio receiving system, arranged and adapted to function in accordance with my invention. It should be understood, however, that this particular system is only shown for illustrative purposes and the invention is not in any sense restricted to the employment of this particular system or, in fact, for use only as a thermionic radio receiving device, sinceit is equally applicable to other types of systems and for other purposes.

The typical illustrative system of Fig. 2 embodies in general a conventional antenna circuit 40, a coupler 42, two variometers 44 and 44, a plurality of thermionic translating devices designated generally as D and A and connected for use as a detector and an audio-frequency amplifier, respectively, an audio-frequency transformer 46, a B battery marked 13, a set of telephone receivers R, an alternating current transformer marked "Transformer, and a source of alternating current energy marked AC.

The two thermionic translating devicesD and A are similar in construction to that shown and already described, although these devices are 11- lustrated diagrammatically in the figure. It will be noted that alternating current energy from a suitable source AC, such as a house-lighting circuit, is supplied to the primary side of the transformer, while one terminal 50 of the secondary side thereof is connected to the heating filament 16 of detector unit D through conductors 52 and 54 and adjustable rheostat 56, whereas the other terminal 58 of the transformer secondary is connected by means of conductor 60 to the shield 18, and also by means of conductors. 6-2 and 64 is connected to ground G.

By this means alternating current energy of low voltage is directly applied to the heating filament of the detector D. The cathode/element proper 20 of the detector D is connected by conductor 66 to the negative terminal of the B battery, which is also connected through conductor 68, variometer 44, secondary winding of the coupler 42 and grid leak to the grid 14. At asuitable point 72 of the B battery, a circuit to the anode or plate 12 is established by means of conductor 74,'primary winding of audio-frequency transformer 46 and variometer 44 The thermionic translating device constituting the amplifier A is connected in a somewhat analogous manner as follows. The terminal 50 of the secondary winding of the transformer is connected to the heating filament 16 by means of conductors ,52 and 76, and adjustable rheostat 78. The shield 18 is connected to the other terminal 58 of the transformer by means of the conductors 60 and to constitute the heating circuit, said shield being connected to ground G by means .of conductors 62 and 64 as is accomplished with respect to the shield of the detector unit. Similarly, the cathode element proper 20 is connected to the negative side of the B battery by means of conductors 66 and 82, while the grid 14 is connected through the secondary winding of audio-frequency transformer 46 to conductor 82 and thence through conductor 66 to the negative tector and amplifier units D and A, the com-' posite cathodes of which are constructed, arranged and operated in the manner already set forth with respect to Fig. 1. Furthermore, the shields of the respective units are also connected to ground, whereby they are maintained at zero potential, thus preventing the possibility of alternating positive and negative potentials being imposed upon the cathode elementsproper, both of which are definitely maintained at negative potentials'by being connected to the negative side of the B battery. The anodes or plates of the respective units are charged positively from the B battery, although the potential on the plate of the detector unit is less than that of the amplifier unit.

Having in mind the various features of construction and operation already set forth, those skilled in the art will readily understand 'the mode of operation of the particular system set forth, and will fully appreciate that the characteristic features of this invention may be easily applied to systems of various types. Without attempting to describe the circuit connections necessitated under such conditions, it is apparent that the present invention, both as a matter of constructionv and as a system of circuit connections, may be embodied and function properly in widely different types of radio circuits. Obviously many modifications 'in'the construction, arrangement, circuit connections and mode of 85 operation may be made, without departing from the spirit and scope of this invention, and therefore, only such limitations should be imposed as are indicated in the appended claims.

What I claim is:

1. A thermionic discharge device comprising an evacuated vessel containing a heating filament, a cathode, an anode, a metal shield maintained' at zero potential disposed between said filament and said cathode in heat-conducting relation with said filament and said cathode but electrically insulated from the latter, and a source of alternating current for supplying heating energy to said filament.

2. A thermionic discharge device comprising an evacuated vessel containing a heating filament, a cathode, an anode, a grounded heatstorage metal shield disposed between said filament and said cathode and in heat-conducting relation with said cathode but electrically insulated therefrom, and a source of alternating current energy for supplying heating energy to said filament. I

3. A thermionic discharge device comprising an evacuated vessel containing a heating filament, a cathode, an anode, a groundedmetal shield closely surrounding said filament and disposed in close proximity to said cathode but electrically insulated therefrom, said filament and said shield being electrically insulated except at their upper ends where they are electrically connected to render the shield a part of the heating circuit for the filament, and a source of alternating current energy connected to one end of said filament and said shield.

4. A thermionic discharge device comprising an evacuated vessel containing a heating filament, a cylindrical metal shield of heat conducting material closely surrounding said filament and electrically insulated therefrom, said filament and 125 said shield being electricaly connected at one end thereof to render the shield a part of the filament circuit, a cylindrical cathode closely surrounding said shield in heat conducting relation therewith but electrically insulated therefrom, a controlling grid and an anode severaly in concentric relation with said cathode, a source of alternating circuit energy connected to one end of said filament and one end of said shield for supplying heating cur-' rent to said filament, a source of direct current energy having its negative terminal connected to said cathode and its positive terminal to said anode, and a ground connection to said shield to maintain it at zero potential with respect to said cathode.

5. A thermionic discharge device comprising an evacuated vessel containing a plurality of electrode elements including a heating filament, a metal shied, a cathode, a grid, and an anode, said shield being disposed intermediate said filament and said cathode, and in heat conducting relation withsaid cathode, and a plurality of electrical connectionsextending from the respective elements within the vessel through its base for detachable connection with extraneous circuits.

6. A thermionic discharge device comprising an evacuated vessel containing a heating filament, adapted to be heated directly by alternating current energy, a shield of relatively great heat storage capacity disposed adjacent said filament in heat conducting relation therewith, a cathode electrically insulated from said shield but in close heating conducting relation therewith whereby the temperature of said cathode is maintained substantially constant and independent of the alternations of the filament heating current, an anode, means for maintaining the anode at positive potential with respect to said cathode and means for maintaining said shield at zero potential with respect to said cathode.

7. A thermionic discharge device comprising an evacuated vessel containing an anode, a controlling grid, and a composite cathode adapted to be maintained at a constant high temperature and constant potential by indirect application of alternating current heating energy, said composite cathode comprising a cathodic element, a filament heated by alternating current and a metal heat storage shield interposed between said filament and said cathodic element in heat-conducting relation therewith but electrically insulatedtherefrom, and means for grounding said shield to maintain it at zero potential.

8. An electron discharge device comprising an evacuated envelope enclosing a tubular anode and a coaxial indirectly heated thermionic cathode mounted inside said tubular anode, said indirectly heated cathode comprising a heater, a tubular metal shield surrounding and electrically insulated from said heater, solid refractory electrical insulation surrounding said metal shield, and an electron emitting cathode element surrounding said solid insulation and in heat conductive relation to said shield and said heater.

9. An electron discharge device comprising an evacuated envelope enclosing an anode, and an indirectly heated cathode comprising a heater, an electron emitting cathode element surrounding said heater, a tubular metal shield interposed between and in heat conducting relation to heater and said cathode element, solid refractory electrical insulation interposed between said shield and said cathode to electrically insulate said cathode element from said shield, and an electrical connection to said metal shield.

10. An electron discharge device comprising an evacuated envelope enclosing an anode and an indirectly heated cathode comprising a heater, a tubular electron emitting cathode element surrounding said heater, a'tubular metal shield interposed between and concentric with said heater and said cathode element, and means for connecting said metal shield to said cathode element to maintain a zone of zero potential between said heater and said cathode element.

WALTER. CLAYPOOLE. 

